J-band absolute magnitude versus color I−J diagram for the five late-M dwarfs with detected lithium. Isochrones and mass tracks from the CIFIST2011 BT-Settl atmosphere models (Allard et al. 2013) are plotted. The lithium region is marked with the blue hatched area. For the objects with no parallax measurements (DENIS0144−4604, DENIS0518−3101, SIPS J1809−7613 and DENIS2022−5645), the open and solid circles represent their absolute magnitudes derived from spectroscopic and kinematic distances, respectively (see Sect. 5.1 for further details). LP 655-48 is also shown (see Sect. 4.2 for discussion).